1. Field of the Invention
The present invention relates, in general, to an electronically controlled brake system for automobiles and, more particularly, to an electronically controlled brake system provided with a pressure accumulator temporarily storing both pressurized oil drained from wheel brakes and pressurized oil outputted from an oil pump.
2. Description of the Prior Art
A conventional brake system for automobiles consists of a booster and a master cylinder, which form braking oil pressure in response to a motion of a brake pedal and feeds the oil pressure to wheel brakes, thus reducing the traveling speed of an automobile or maintaining a stopped state of the automobile. However, the automobiles with such conventional brake systems may slip over a road in accordance with road surface conditions or variations in oil pressure during a braking operation.
In an effort to overcome such a problem, a variety of electronically controlled brake systems, such as an anti-lock brake system (ABS), a traction control system (TCS) and an active brake control system (ABCS), have been proposed and widely used. The ABS electronically controls the oil pressure fed to wheel brakes and prevents slippage of wheels during a braking operation. The TCS is designed to prevent excessive slippage of drive wheels during quick drive or sudden acceleration. The ABCS controls oil pressure in accordance with the traveling speed and steered angle of an automobile, thus securing the traveling stability while driving the automobile. FIG. 1 is a hydraulic circuit diagram of a conventional ABCS provided with an electronic stability program (ESP).
As shown in FIG. 1, the conventional ABCS consists of a plurality of solenoid valves 2a and 2b, which control a flow of pressurized oil fed to wheel brakes 1. The ABCS also has a low-pressure accumulator 3, which temporarily stores pressurized oil drained from the wheel brakes 1 during an ABS pressure reducing mode. An oil pump 4 sucks the pressurized oil from the low-pressure accumulator 3, and outputs the oil. A shuttle valve 6 is mounted on an oil suction line, which branches from the inlet line of the pump 4 and extends to the pressure inlet port 5a of a master cylinder 5. The shuttle valve 6 thus selectively opens or closes the oil suction line. A traction control solenoid valve 7 is mounted on an oil line, which extends from the inlet of the pump 4 to the pressure inlet port 5a of the master cylinder 5. The above valve 7 thus selectively opens or closes the oil line. The ABCS further includes an intermediate pressure accumulator 8, which temporarily stores pressurized oil fed from the pump 4. An electronic control unit (not shown) is included in the ABCS, and controls the electronic parts of the ABCS.
Of the solenoid valves 2a and 2b, each of the first valves 2a is an NO(normal open)-type solenoid valve and mounted on an oil line at an upstream position before an associated wheel brake 1, while each second valve 2b is an NC(normal close)-type solenoid valve and mounted on the oil line at a downstream position after the wheel brake 1. The two types of solenoid valves 2a and 2b are operated under the control of the electronic control unit. That is, the electronic control unit senses the traveling speed of an automobile, and controls the two types of solenoid valves 2a and 2b in accordance with sensed traveling speed of the automobile.
The low-pressure accumulator 3 is independently arranged in the hydraulic circuit of the ABCS while being commonly connected to the downstream lines of the two NC-type solenoid valves 2b, thus temporarily storing pressurized oil drained from the wheel brakes 1 during an ABS pressure reducing mode.
The intermediate-pressure accumulator 8 feeds pressurized oil to the inlet of the oil pump 4 during a TCS mode or an ESP mode. The above accumulator 8 is connected to a bypass line 8a, which bypasses pressurized oil, outputted from the pump 4, to the inlet side of the pump 4. An additional NC-type solenoid valve 9a is mounted on the bypass line 8a at a downstream position after the intermediate-pressure accumulator 8, and opens the bypass line 8a during a TCS mode or an ESP mode. A relief valve 9b is mounted on the bypass line 8a at an upstream position before the intermediate-pressure accumulator 8. This relief valve 9b returns excessively pressurized oil to the master cylinder 5 during a TCS mode or an ESP mode.
The solenoid valves 2a and 2b, oil pump 4, low-pressure accumulator 3, intermediate-pressure accumulator 8, and relief valve 9b are compactly set in a single hydraulic block (not shown), which is made of aluminum to form a cubic shape.
However, the conventional ABCS must separately set the low-pressure accumulator 3 and the intermediate-pressure accumulator 8 in the hydraulic block, since it is necessary to temporarily store pressurized oil, drained from the wheel brakes 1 during an ABS pressure reducing mode, in the low-pressure accumulator 3, and feed pressurized oil from the intermediate-pressure accumulator 8 to the inlet of the oil pump 4 during a TCS mode or an ESP mode. Due to the two accumulators 3 and 8 separately set in the hydraulic block, it is only limitedly possible to accomplish desired compactness of the hydraulic block, in addition to an increase in the production cost of the ABCS.
Furthermore, upsetting noises are generated when pressurized oil passes through the relief valve 9b during a process of feeding the pressurized oil to the intermediate-pressure accumulator 8.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an electronically controlled brake system for automobiles, the low-pressure accumulator of which is integrated with the intermediate-pressure accumulator into a single body, thus accomplishing desired compactness of the brake system and reducing the production cost of the brake system.
In order to accomplish the above objects, the present invention provides an electronically controlled brake system for automobiles, comprising: an NO-type solenoid valve arranged at an upstream line of a wheel brake and controlling a flow of pressurized oil fed from both a master cylinder and an outlet of an oil pump to the wheel brake; an NC-type solenoid valve arranged at a downstream line of the wheel brake and controlling a flow of pressurized oil discharged from the wheel brake; an oil suction line connecting the master cylinder to the inlet of the oil pump and feeding pressurized oil from the master cylinder to the oil pump during a TCS mode; an NC-type shuttle valve mounted on the oil suction line to open or close the oil suction line; and a low/intermediate pressure accumulator connected to both the outlet of the NC-type solenoid valve and the oil suction line so as to store the pressurized oil discharged from the wheel brake during an ABS pressure reducing mode, and feed the stored pressurized oil to the inlet of the oil pump during an ABS pressure increasing mode, the pressure accumulator also storing the pressurized oil outputted from the oil pump to feed the stored pressurized oil to the inlet of the oil pump during an ESP mode.
The brake system of this invention further comprises: an oil charging line extending from the outlet of the oil pump to the low/intermediate pressure accumulator; a first control valve mounted on the oil charging line to open or close the oil charging line; an oil feeding line branching from the oil charging line at a downstream position after the first control valve and connected to the oil suction line at a downstream position after the NC-type shuttle valve; and a second control valve mounted on the oil feeding line to open or close the oil feeding line such that the oil feeding line is opened during the ESP mode so as to feed the pressurized oil from the low/intermediate pressure accumulator to the inlet of the oil pump.
In the brake system, wherein the first and second control valves are NC-type solenoid valves.
In the brake system, the first control valve is a check valve which is opened when pressure of oil outputted from the oil pump is not lower than a predetermined reference level, and which prevents an inverse flow of pressurized oil charged in the low/intermediate pressure accumulator.
The low/intermediate pressure accumulator comprises: a cylinder receiving pressurized oil therein; a piston received in the cylinder to extend from or retract into the cylinder in accordance with a flow of pressurized oil into or from the cylinder; an elastic member elastically supporting the piston; and a position sensor sensing a movement of the piston exceeding a predetermined stroke, whereby the position sensor stops an operation of the oil pump when the piston moves by a length exceeding the predetermined stroke during an oil charging mode.
In the brake system, a check valve is mounted on an oil line extending from the inlet of the oil pump to the low/intermediate pressure accumulator. This check valve thus opens the oil line to feed pressurized oil from the low/intermediate pressure accumulator to the inlet of the oil pump when pressure of the pressurized oil discharged from the wheel brake to the low/intermediate pressure accumulator during the ABS pressure reducing mode is not lower than a predetermined reference level.